Thermodynamics of aqueous gallium chloride. Apparent molar volumes and heat capacities at 25°C

Abstract

Apparent molar volumes and heat capacities of aqueous GaCl₃ have been measured at 25°C in binary GaCl₃ solutions up to 3 mol-kg⁻¹, and in ternary GaCl₃-HCl solutions, containing 0.1345 mol-kg⁻¹ HCl to suppress hydrolysis, up to a concentration of 1 mol-kg⁻¹ GaCl₃. Using the Pitzer interaction model for the excess properties, and using ridge regression for the derivation of physically meaningful regression parameters, the measurements yield the following results for the standard molar properties and Pitzer parameters at 25°C: V⁰(GaCl₃)=12.85 cm³-mol⁻¹;β ^v₀ (GaCl₃)=1.10×10⁻⁴ kg-mol⁻¹−J⁻¹−cm⁻³; β ¹_v (GaCl₃)=2.12×10⁻³ kg−mol⁻¹−J⁻¹−cm³; Cv(GaCl₃)=1.34×10⁻⁵ kg²−J⁻¹−cm³; V^o(GaOHCl₂)=13.84 cm³−mol⁻¹; C ^p_o (GaCl₃)=−480.8 J−K⁻¹−mol⁻¹; β ⁰_J (GaCl₃)=−8.02×10⁻⁶ kg−mol⁻¹−K⁻²; β ¹_J (GaCl₃)=0.73×10⁻⁴ kg−mol⁻¹−K⁻²; C_J(GaCl₃)=−2.52×10⁻⁶ kg²-mol⁻²-K⁻²; C ⁰_p (GaOHCl₂)=20.4 J-K⁻¹-mol⁻¹. The latter parameter has only mathematical significance, its physical meaning is unclear. Comparison of the present experimental results for the standard molar properties of Ga³⁺ with semi-empirical correlations casts doubt upon the general validity of these correlation methods for trivalent cations.